1. Field of the Invention
The present invention relates to a method of recording a digital signal suited to the reproduction of recorded signals with few errors by accurately tracing the recording tracks formed on a recording medium.
2. Description of the Prior Art
When recording a digital signal magnetically on a narrow track, presently, in order to track accurately and reproduce the signals with fewest errors, pilot tones of several different frequencies are superposed in each track of the data to be recorded at the time of recording. For example, as shown in FIG. 2, using pilot tones of four different frequencies, a case of recording on a magnetic tape is explained below. In this case, the recording tracks continuously formed on the recording medium (hereinafter called tracks) are sequentially supposed to be T1, T2, T3, T4, and so forth. Besides, the frequency of the pilot tone to be superposed on track T1 is supposed to be f1 (Hz), the frequency of the pilot tone to be superposed on track T2 is to be f2 (Hz), the frequency of the pilot tone to be superposed on track T3 is to be f3 (Hz), and the frequency of the pilot tone to be superposed on track T4 is to be f4 (Hz). The pilot tone frequencies fl to f4 are recycled in a period of four tracks, and are superposed on each track.
When reproducing, for example relating to track T2, by sampling and comparing the crosstalk levels of the pilot tones (f1 Hz, f3 Hz) from the both side tracks T1 and T3, the tracking is controlled so that both levels are identical. In other words, it is controlled so that the center of the reproducing head When tracing the track T2 may correctly trace the center of the track T2. Then, by sampling and comparing the crosstalk levels of both side pilot tones (f2 Hz, f4 Hz) while scanning the track T3, the tracking is controlled so that both levels are identical. Similarly, while scanning the track T4, the crosstalk levels of the pilot tones (f3 Hz, f1 Hz) are compared. While scanning the track T5, the crosstalk levels of the pilot tones (f4 Hz, f2 Hz) are sampled and compared to control the tracking. The crosstalk of each pilot tone is extracted by a band-pass filter from a reproduced signal.
In such a constitution, in order to track accurately, the crosstalk level of the pilot tone of such an extent as to not be easily affected by noise must be detected by the bandpass filter to compare the levels. Or, for the pilot tone to be detected, the data components of the pertinent frequency may be also be regarded as noise. Therefore, the recording level of the pilot tone must be higher than the level of the data signal by about more than ten to twenty decibels. However, when a pilot tone of such a high level is superposed on the data signal in an analog fashion, it is equivalent to noise as seen from the data signal, and errors increase in the reproduced data. Or, to avoid this, when a pilot tone of a high level is digitally added to the data signal, generally, the recording rate increases, thereby making it difficult to record and reproduce.